The long term objective of this research proposal is to identify the viral and cellular components involved in cell fusion mediated by herpes simplex virus (HSV). An intimate understanding of cell fusion induced by HSV may facilitate effective treatments to prevent such cell-to-cell spread in infected individuals. An understanding of cell-to-cell fusion mediated by HSV may also provide insight into virus-to-cell fusion because the two processes require overlapping sets of proteins. This proposal outlines three different approaches to identify cellular or viral proteins that interact with the mutant or wild-type forms of two envelope glycoproteins of HSV-1 required for cell fusion, gB and gH. The first approach will be to utilize the two-hybrid system in yeast to identify gB- or gH-interacting proteins. The two-hybrid system is a genetic screen performed in yeast expressing a cDNA library to discover viral or cellular proteins that interact with mutant or wild-type cytoplasmic domains of gB or gH. The second approach will be to attempt to co-immunoprecipitate cellular or viral proteins that are interacting with mutant or wild-type forms of gB or gH in infected cells. The third approach will be to fuse mutant or wild- type versions of the cytoplasm tail of gB or gH to glutathione-S- transferase and determine if cellular or viral proteins will bind to such fusion proteins that are immobilized on columns.